Steering system

ABSTRACT

A steering system for an articulated steered mobile work machine has a first sensor for sensing the relative angular position of first and second machine sections and a second sensor for sensing the relative angular position of second and a third machine sections. A controller determines for a sensed relative angle of the first and second machine sections the desired relative steering angle of the second and third sections and actuates a second control valve to direct fluid flow to a second pair of fluid operated jacks and pivot the third machine section to a desired angular position relative to the second machine section. The second sensor provides feedback as to the relative angular position of the second and third machine sections.

TECHNICAL FIELD

This invention relates to a steering system for an articulated steeredmobile machine and more particularly to a steering system forautomatically controlling a second pair of steering jacks in response toa relative steered angle position of pivotally connected first andsecond machine sections.

BACKGROUND ART

Articulated steering has been provided on work machines for many years.Such steering systems typically include a pair of fluid operated jacksconnected between a pair of pivotally connected machine sections of thework machine. The jacks are extensibly movable to relatively pivot themachine sections and effect steering of the machine as it traverses theunderlying terrain. The jacks are normally positioned on opposite sidesof the pivot and a longitudinal machine axis so that extension of onejack and retraction of the other causes the articulated steering.

It has been known to provide multiple articulated steered machinesections on certain machines. For example, a forwarder used incollecting and carrying logs in forestry applications often has threeconsecutively pivotally connected machine sections. An example of such amachine is shown in U.S. Pat. No. 5,366,337, to Peter Eriksson, datedNov. 22, 1994. In such machines, the first and second pairs of fluidoperated steering jacks are separately controlled. Since there is nocoordination between the steering of the first and second relativelysteered machine sections and the second and third relatively steeredmachine sections, the steering radius of the pivotally connected firstand second sections of the machine may differ from the steering radiusof the pivotally connected second and third sections of the machine.This difference may, in extreme situations, cause excessive tire wear,increased fuel consumption, and reduced accuracy of machinecontrollability.

In some machine applications, the second pair of jacks has beeneliminated, and the third section is allowed to trail the secondsection. This reduces the potential for gross forced steeringmisalignment but eliminates the ability to steer the third machinesection, an advantage in rough terrain applications. In free trailingapplications, the third section may wander and deviate from the optimumtrailing location. In forwarder machine applications, improperpositioning of the third section increases the amount of time to loadlogs. Also, such free following is detrimental to overall machinestability.

It is recognized that there are situations where independent articulatedsteering of the pivotally connected machine sections, free trailing ofthe pivotally connected machine sections, and optimized path controlledsteering of the following machine section(s) are each desirable. Atpresent, no steering system available is capable of providing controlledpath articulated steering for the trailing section, or a combination ofthe above.

The present invention is directed to overcoming one or more of theproblems set forth above.

DISCLOSURE OF THE INVENTION

A steering system for a mobile machine having first, second and thirdconsecutively connected relatively pivotal machine sections, a firstpair of fluid operated extensible steering jacks connected between saidfirst and second machine sections and a second pair of extensible fluidoperated steering jacks connected between said second and third machinesections is provided. A first sensor connected to said machine sensesthe actual relative steering angle position of the first and secondmachine sections and delivers a corresponding first actual steeringangle signal. A second sensor connected to said machine senses theactual relative steering angle position of the second and third machinesections and delivers a corresponding second actual steering anglesignal. A controller connected to the first and second sensors receivesthe first and second actual steering angle signals, determines a desiredrelative steering angle position of the second and third sections basedon the first actual steering angle signal, and delivers a correctingsteering angle signal in response to a difference between the desiredand actual relative steering angles of the second and third sections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic top plan view of an embodiment of anarticulated steered mobile work machine the present invention;

FIG. 2 is a diagrammatic side view taken along lines 2--2 of FIG. 1.

FIG. 3 is a diagrammatic top plan view of the mobile work machine ofFIG. 1 with first, second and third articulated steered machine sectionsfollowing an optimum articulated steering path;

FIG. 4 is a diagrammatic schematic drawing of a steering control systemprovided on the mobile work machine;

FIG. 5 is diagrammatic schematic drawing of the steering control systemof FIG. 4 showing additional details; and

FIG. 6 is a diagrammatic schematic drawing of a fluid control system andsteering jacks of the steering control system.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, and particularly FIGS. 1 and 2, a mobilework machine 10 having first, second, and third consecutively pivotallyconnected articulated steered machine sections 12,14,16 is shown. Thefirst and second machine sections 12,14 are pivotal about a firstelevationally oriented axis 18 and the second and third machine sections14,16 are pivotal about a second elevational axis 20. The mobile workmachine 10 is shown as a forwarder used in tree harvesting applications,however, other mobile work machines 10 having pivotally connectedsections are considered equivalents and within the scope of theinvention. The mobile work machine 10 has a plurality of ground engagingwheels 22, one pair connected to each of the sections, and a prime mover24 connected to deliver motive power to the ground engaging wheels 22 inany suitable manner, for example, by a hydraulic wheel motor drivesystem.

A steering system 25 includes a first pair of steering jacks 26pivotally connected in a conventional manner between the first andsecond sections 12,14 and a second pair of steering jacks 28 pivotallyconnected in a conventional manner between the second and third sections14,16. The steering jacks 26,28 each have (FIG. 6) a rod end 30, and ahead end 32 and are extensibly movable in response to the application ofpressurized fluid flow to the rod and/or head ends. The first pair ofsteering jacks 26 are effective to cause the first and second machinesections to pivot relative to each other about the first elevationalaxis 18. The second pair of steering jacks are effective to cause thesecond and third machine sections 14,16 to pivot relative to each otherabout the second elevational axis 20. This relative controlled pivotalmovement (articulation) of the first and second machine sections 12,14,and second and third machine sections 14,16 steers the machine 10 and isoften referred to as articulated steering.

As best seen in FIG. 6, a fluid control system 34 of the steering system25 is connected to the first and second pairs of fluid operated jacks26,28 and actuatable to selectively direct pressurized fluid flow to thefluid operated jacks 26,28. The fluid control system 34 includes a pump36, a reservoir 38 and first and second electrically operated controlvalves 40,42. The first and second control valves 40,42 are preferablyinfinitely variable and movable from a neutral position 44 to aselective one of first and second fluid directing positions 46,48. Thefirst electrically operated control valve 40 is connected to communicatefluid flow between the first pair of fluid operated jacks 26, the pump36 and the reservoir 38. The second electrically operated control valve42 is connected to communicate fluid flow between the second pair offluid operated jacks 28, the pump 36 and the reservoir 38.

The first control valve 40 is connected to the head end 32 of a firstjack 50 of the first pair of jacks 26 and to the rod end 30 of a secondjack 52 of the first pair of jacks 26 by a conduit 54. The first controlvalve 40 is also connected to the rod end 30 of the first jack 50 and tothe head end 32 of the second jack 52 by a conduit 56.

The second control valve 42 is connected to the head end 32 of a firstjack 58 of the second pair of jacks 28 and to the rod end 30 of a secondjack 60 of the second pair of jacks 28 by a conduit 62. The secondcontrol valve 42 is also connected to the rod end 30 of the first jack58 of the second pair of jacks 28 and to the head end 32 of the secondjack 60 of the second pair of jacks 28 by a conduit 64.

The first control valve 40 delivers pressurized fluid flow from the pump36 to the rod end 30 of first fluid operated jack 50 of the first pair26 and to the head end 32 of the second fluid operated jack 52 of thefirst pair 26 at the first position 46. The first control valve 40 alsodelivers pressurized fluid flow from the pump 36 to the rod end 30 ofthe second fluid operated jack 52 of the first pair 26 and to the headend 32 of the first fluid operated jack 50 of the first pair 26 at thesecond position 48. Excess fluid flow exhausted from the first andsecond jacks 50,52 is directed to the reservoir 38 by way of anappropriate one of the first and second conduits 54,56 in a conventionalmanner.

The second control valve 42 delivers pressurized fluid flow from thepump 36 to the rod end 30 of the first fluid operated jack 58 of thesecond pair 28 and to the head end 32 of a second fluid operated jack 60of the second pair 28 at the first position 46. The second control valve42 also delivers pressurized fluid flow from the pump 36 to the rod end30 of the second fluid operated jack 60 of the second pair 28 and to thehead end 32 of the first fluid operated jack 58 of the second pair 28 atthe second position 48.

As best seen in FIGS. 1-4, the steering system 25 includes a firstsensor 66 connected to the machine 10 at a location adjacent the firstelevational axis 18. The first sensor 66 senses the actual relativesteering angle position of the first and second machine sections 12,14and delivers a corresponding first actual steering angle signal.

A second sensor 68 of the steering system 25 is connected to the machine10 at a location adjacent the second elevational axis 20. The secondsensor 68 senses the actual relative steering angle position of thesecond and third machine sections 14,16 and delivers a correspondingsecond actual steering angle signal. The first and second sensors 66,68are shown as analog signal producing devices, for example, apotentiometer. However, digital devices, such as, optical encoders,magnetic transducers and the like are equivalents and considered withinthe scope of the invention.

Referring to FIGS. 4 and 5, the steering system 25 includes a controller70 connected to the first and second sensors 66,68 by electricalconductors 72,74 and receives the first and second actual steering anglesignals by way of the conductors 72,74. The controller 70 determines adesired relative steering angle position of the second and thirdsections 14,16 based on the first actual steering angle signal anddelivers a correcting steering angle signal in response to a differencebetween the desired and actual relative steering angles of the secondand third sections 14,16.

The fluid control system 34 is connected to the controller 70 and isresponsive to the delivery of the correcting steering angle signal todirect pressurized fluid flow to the second pair of fluid operated jacks28 in response to the delivery of the correcting steering angle signal.The position to which the second control valve 42 is shifted is afunction of the sense (+ or -) of the control signal being delivered.

The controller 70 includes a computer 76 having a processor 78, a memory80, and an I/O port 82. The controller 70 may also include an analog todigital (A/D) converter 84 in applications where analog signalingdevices are used and where analog signals are provided to the controller70. The controller 70 also includes a driver circuit 86 which isconnected to the computer 76 and to the solenoids 88,90 of the first andsecond electrically operated control valves 40,42 by conductors 92,94.The driver circuit 86 is of a conventional design and responds tosignals delivered from the computer 76 to actuate either one or of bothof the first and second electrically operated control valves 40,42. Itshould be recognized that the computer 76 herein described includesequivalent discrete electronic components of any suitable arrangementcapable of performing the desired logic functions in either an open orclosed loop.

The processor 78 receives the first and second steering angle signals,and based on the first actual steering angle signal, determines thedesired relative steering angle of the second and third machine sections14,16. This determination is made in accordance with preprogrammedinstructions and information 96 stored in memory 80. Information 96includes data, maps, look-up tables and the like. The processor 78compares the desired relative steering angle of the second and thirdmachine sections 14,16 with the actual relative steering angle of thesecond and third machine sections 14,16 and delivers the correctingsteering angle signal in response to the difference between the desiredand actual relative steering angle being greater than a preselectedamount. The preselected amount is an accepted error and tolerancedetermined either mathematically or empirically and considers factorssuch as speed of machine operation, terrain and other operationparameters.

As shown in FIG. 3, a predetermined optimum turning arc 98 is shown fora given machine 10 configuration and size. The radius of the arc isdetermined as a function of the relative steering angle (turning radius)of the first and second machine sections 12,14. The relative steeringangle of the second and third machine sections 14,16 is based on theturning angle of the first and second machine sections. The first andsecond elevational axes 18,20, and a third elevational axis 100 locatedtransversely midway on the third machine section at a location on thethird section spaced from the second axis, intersects the curve when therelative steering angle of the second and third sections 14,16 is at anoptimum angle.

The correcting steering angle signal is delivered to the driver 86. Thiscauses actuation of the second electrically operated control valve 42based on the correcting steering angle signal. The driver circuit 86 isconnected to a solenoid of each of the first and second electricallyoperated control valves 40,42 by electrical conductors 92,94. Thesolenoids 88,90 respond to electrical energy delivered by the drivercircuit 86 and shift the first and second valves 40,42 to appropriateones of the first and second positions 46,48. The second electricallyoperated control valve 42 is shifted to one of the first and secondpositions 46,48 in response to the delivery of the correcting steeringangle signal.

Referring to FIG. 5, the steering system 25 includes an operator inputarrangement 101 by which the vehicle operator selects various steeringoptions and makes steering maneuvers. The operator input arrangement 101includes a steering selector device 102 connected to the first andsecond electrically operated control valves 40,42. The steering selectordevice 102 is movable to selectively controllably move the first andsecond electrically operated control valves 40,42 to the first andsecond positions 46,48. In particular, the steering selector device 102is connected by an electrical conductor 104 to the controller 70, anddelivers a steering command signal to the controller 70 in response tomovement thereof. The controller 70, based on the steering commandsignal delivered, responds and causes the driver circuit 86 to deliver asteering control signal to shift one or both of the first and secondelectrically operated control valves 40,42 to an appropriate one of thefirst and second positions. The steering selector device 102 is shown asan analog device, for example, a potentiometer connected to the A/Dconverter. It is to be understood that digital devices of anyappropriate type, for example, an encoder, a magnetic device or the likemay be substituted therefor without departing from the sprit of theinvention.

A steering mode switch 106 of the input arrangement 101 is connected tothe controller 70 by a conductor 108. The steering mode switch 106 ismovable between a first steering mode position at which the controlleris conditioned to block the passing of a steering control signal to thesecond electrically operated control valve 42 and a second steering modeposition at which the controller 70 is conditioned to pass the steeringcontrol signal to the second electrically operated control valve 42. Thesteering mode switch 106 provides the capability of selecting eitherrelative pivotal steering of only the first and second pivotallyconnected machine sections 12,14 or of both the first and second 12,14,and second and third 14,16 pivotally connected machine sections. It isto be recognized that the previously discussed steering selector device102 may be movable to other positions at which steering signals aredelivered to the controller 70 to control the second control valve 42independently of the first control valve 40 and facilitate preliminarypositioning of the third machine section 16 relative to the secondmachine section 14.

An automatic-manual mode switch 110 is connected to the controller 70 byelectrical conductor 112. The automatic-manual mode switch 110 ismovable between an automatic mode position at which the correctingsteering angle signal is free to pass from the controller 70 and amanual mode position at which the correcting steering angle signal isblocked from passing from the controller 70. The automatic-manual modeswitch 110 delivers either an enabling or disabling signal to thecontroller 70 depending on the position selected. When theautomatic-manual mode switch 110 is at the automatic mode position,actuation of the second steering jacks 28 by the steering selector 102is prevented at the controller 70.

As shown in FIG. 6, an electrically operated float valve 114 isconnected to the reservoir 38, the second pair of fluid operated jacks28, and the controller 70. The float valve 114 has a float position 116at which the head and rod ends 32,30 of the second pair of fluidoperated steering jacks 28 is connected to the reservoir 38. The floatvalve 114 also has an open position 118 at which fluid flow is freelydelivered between the second electrically operated control valve 42 andthe second pair of fluid operated steering jacks 28. The float valve 114has a solenoid 120 and is spring biased to the open position 118. Thesolenoid 120 of the float valve 114 is connected to the driver 86 by anelectrical conductor 122 and the float valve 114 is movable to the floatposition in response to receiving an electrical signal from thecontroller 70.

A float switch 124 is connected to the controller 70 by an electricalconductor 126. The float switch 124 is movable between a first positionat which a float signal is delivered to the controller 70 and a secondposition at which the float signal is blocked from the controller 70.The float valve 114 moves to the float position 116 in response to thefloat switch 124 being at the first position. The controller 70 deliversan electrical signal to the float valve 114 and moves the float valve114 to the float position 116 in response to the float switch 124 beingat the first position. The controller 70 disables the passing of asteering control signal to the second electrically operated controlvalve 42 in response to the float switch 124 being at the firstposition. The controller 70 also prevents the passing of the correctingsteering angle signal to the second electrically operated control valve42 in response to the float switch 124 being at the first position.

INDUSTRIAL APPLICABILITY

With reference to the drawings and in operation, the machine operatorsimply selects the mode of steering desired for the particular workapplication and uses the steering selector 102 to steer the machine overthe underlying terrain.

In certain applications, the operator is interested in having singlearticulated joint steering about the first elevational axis 18. Toachieve this, the operator simply places the steering mode switch 106 atthe first position. This conditions the controller 70 to block steeringcontrol signals to the second electrically operated steering valve 42and deliver steering control signals to only the first electricallyoperated control valve 40. As a result, controlled steering occurs onlyabout the first elevational axis 18 and between the first and secondmachine sections 12,14.

In other applications, the machine operator desires controlled steeringof all the machine sections 12,14,16, pivotal movement about both thefirst and second elevational axes 18,20. This is achieved simply byplacing the steering mode switch 106 at the second position. Input fromthe selector 102 is then processed by the controller 70 and delivered tocontrol both the first and second electrically operated control valves40,42.

In some applications, the machine operator is interested in enabling thethird machine section 16 to simply follow the second machine section 14with a preselected amount of restriction to free movement. To achievethis, the operator simply places the float switch 124 at the firstposition. This results in the controller 70 delivering a float signal tothe float valve 114 and moving the float valve to the float position116. At the float position 116, the second pair of fluid operated jacks28 are open to the reservoir 38 and free to extend and retract with thepreselected amount of resistance.

An automatic mode of operation of the steering system 25 is provided. Inthe automatic mode of operation, the optimum steering angle of thesecond and third machine sections 14,16 based on the actual steeringangle of the first and second machine sections 12,14 is determined. Thefluid control system 34 articulates the second and third machinesections 14,16 to the optimum steering angle position. To achieve this,the operator simply moves the automatic-manual mode switch 110 to theautomatic mode position. The computer 76, based on information from thefirst and second sensors 66,68, processes the steering angle positioninformation in accordance with the preprogrammed instructions,determines the desired (optimum) relative steering angle of the secondand third machine sections 14,16 based on the relative steering angle ofthe first and second machine sections 12,14, and delivers the correctingsteering angle signal to the second electrically operated control valve42. The second control valve 42 shifts to the appropriate one of thefirst and second positions 46,48, as determined by the sense of thesignal, in response to there being a difference between the actualrelative steering angle of the second and third machine sections and thedesired steering angle of the second and third machine sections 14,16.The second pair of fluid operated steering jacks 28 relatively moves thesecond and third machine sections 14,16 in response to fluid flowdirected by the second control valve 42.

As discussed above, certain modes of operation, are disabled to higherpriority functions under certain conditions. For example, to mentionjust a few, the controller 70 disables the passing of a steering controlsignal to the second electrically operated control valve 42 when thefloat switch 124 is at the first position, and disables the passing ofthe correcting steering angle signal to the second electrically operatedcontrol valve 42 in response to the float switch 124 being at the firstposition.

Other aspects, objects and advantages of the present invention can beobtained from a study of the drawings, the disclosure and the appendedclaims.

We claim:
 1. An articulated steered mobile machine, comprising:first,second and third machine sections, said second machine section beingpivotally connected to said first machine section and said third machinesection being pivotally connected to said second machine section; afirst pair of fluid operated steering jacks connected between said firstand second machine sections, said first pair of fluid operated steeringjacks being extensible movable to pivot said first and second machinesections relative to each other; a second pair of fluid operatedsteering jacks connected between said second and third machine sections,said second pair of steering jacks being extensible movable to pivotsaid second and third pivotal machine sections relative to each other,said first and second pairs of fluid operated jacks each having a headend and a rod end; a fluid control system connected to said first andsecond pairs of fluid operated jacks and being actuatable to selectivelydirect pressurized fluid flow to said fluid operated jacks, said fluidcontrol system having a pump, a resrvoir, a first electrically operatedcontrol valve connected to the pump and the first pair of fluid operatedjacks, and a second electrically operated control valve connected to thepump and the second pair of fluid operated jacks; a first sensorconnected to sense an actual relative steering angle position of thefirst and second machine sections and deliver a corresponding firstactual steering angle signal; a second sensor connected to sense anactual relative steering angle position of the second and third machinesections and deliver a corresponding second actual steering anglesignal; a controller connected to the first and second sensors and tosaid fluid control system, said controller receiving said first andsecond actual steering angle signals, determining a desired relativesteering angle position of the second and third sections based on thefirst actual steering angle signal, and delivering a correcting steeringangle signal in response to a difference between the desired and actualrelative steering angles of the second and third sections, said fluidcontrol system directing pressurized fluid flow to the second pair offluid operated jacks in response to receiving the correcting steeringangle signal; said first control valve being movable to a first positionat which pressurized fluid flow is directed from the pump to the rod endof a first of the fluid operated jacks of the first pair and to the headend of a second fluid operated jack of said first pair, and to a secondposition at which pressurized fluid flow is directed from the pump tothe rod end of the second fluid operated jack of the first pair and tothe head end of the first fluid operated jack of the first pair; saidsecond control valve being movable to a first position at whichpressurized fluid flow is directed from the pump to the rod end of afirst of the fluid operated jacks of the second pair and to the head endof a second fluid operated jack of said second pair, and movable to asecond position at which pressurized fluid flow is directed from thepump to the rod end of the second fluid operated jack of the second pairand to the head end of the first fluid operated jack of the second pair,said second control valve being shifted to one of the first and secondpositions in response to receiving said correcting steering anglesignal; a steering selector device connected to said first and secondelectrically operated control valves, said steering selector devicebeing movable to selectively controllably move the first and secondelectrically operated control valves between said first and secondpositions, a steering control signal being delivered to at least one ofthe first and second electrically operated control valves in response tomovement of the steering selector device, said steering selector beingconnected to the controller and delivering a steering command signal inresponse to movement thereof, said controller delivering a steeringcontrol signal to at least one of the first and second electricallyoperated control valves in response to receiving the steering commandsignal; an electrically operated float valve connected to saidreservoir, said second pair of fluid operated jacks, and saidcontroller, said electrically operated float valve having a floatposition at which the head and rod ends of the second pair of fluidoperated steering jacks are connected to said reservoir, said floatvalve and being selectively movable to the float position; and a floatswitch connected to the controller and movable between a first positionat which a float signal is delivered to the controller and a secondposition at which the float signal is blocked from the controller, saidfloat valve moving to the float position in response to the float switchbeing at the first position.
 2. The articulated steered mobile machine,as set forth in claim 1, wherein said controller disabling the passingof a steering control signal to the second electrically operated controlvalve in response to said float switch being at the first position. 3.The articulated steered mobile machine, as set forth in claim 1, whereinsaid controller disabling the passing of the correcting steering anglesignal to the second electrically operated control valve in response tothe float switch being at the first position.